1. Field of the Invention
The present invention relates to a method for setting laser power of an optical disc device, and more particularly to a method for setting laser power of an optical disc device in which power setting data is detected when no power setting data is present in the device and the laser power is set based on the detected power setting data.
2. Description of the Related Art
Optical disc devices require a variety of laser power levels according to their operating modes such as data recording and playback modes. Thus, typically, a laser power setting operation is performed for each optical disc device in the manufacturing process to detect and store data (power curve data) necessary for setting a laser power of each operating mode.
FIG. 1 illustrates a structure, associated with an optical disc device, for detecting power curve data required for laser power setting of the optical disc device. Generally, it is possible to set a desired laser power level by adjusting an input voltage DAC voltage applied to an R/F unit 50 in FIG. 1 through a D/A converter 40. The input voltage DAC and an output laser power P obtained therefrom are proportional to each other as represented by a line in FIG. 2 with an offset determined based on the characteristics of a laser diode and a laser drive IC in the optical disc device.
The laser power setting process includes a process for obtaining the relationship between the input voltage DAC and the output laser power, i.e., obtaining an equation of a line representing the relationship. A DAC_Offset value and a gradient of the line must be known in order to obtain the line equation. If a laser power P1 corresponding to a given input voltage DAC1 and the DAC_Offset value are known, it is possible to obtain the gradient of the line.
Accordingly, in the laser power setting operation performed in the manufacturing process of the optical disc device, the laser power P1 corresponding to the given input voltage DAC1 and the DAC_Offset value are detected, and the detected values are stored, as power curve data, in a memory (a flash ROM or an EEPROM) of the optical disc device. The following is a description of a conventional laser power setting operation for detecting the power curve data.
In the manufacturing process of the optical disc device, an operator or manager instructs activation of a laser power setting operation through a host so that a DAC_Offset value for laser power setting is detected and stored when the optical disc device enters a laser power setting mode. The DAC_Offset value is an input value applied to the D/A converter 40 at the moment when the R/F unit 50 produces an output voltage. When an X axis represents the DAC value and a Y axis represents the laser power or a feedback voltage level FPDO, the DAC_Offset value corresponds to an x-intercept of a first degree equation.
The DAC_Offset value can be detected using a first degree equation determined by specific input voltages DAC1 and DAC2, laser powers P1 and P2 output from or voltage levels FPDO1 and FPDO2 fed back from the optical pickup 60 receiving the input voltages DAC1 and DAC2. The following is an equation for detecting the DAC_Offset value using the input voltages DAC1 and DAC2 and the laser powers P1 and P2 actually output in response to the input voltages.DAC_Offset={(P2×DAC1)−(P1×DAC2)}/(P2−P1)
Even when the same input voltage is applied, different laser powers maybe output according to different characteristics of optical pickups 60 and R/F units 50. Thus, conventionally, in the manufacturing process of optical disc device sets (hereinafter, also referred to as “sets” for short), not only the DAC_Offset value but also an actual laser power P1 output in response to the specific input voltage DAC1 are determined for each set. Conventionally, to obtain the relationship between a specific input voltage and an actual laser power output in response to the specific input voltage, equipment such as a laser power meter 20 and a special tool 30 is used to actually measure the output laser power.
In the manufacturing process of each set, when power curve data required for laser power setting is obtained, i.e., when a DAC_Offset value and a laser power P1 actually output in response to the specific input voltage (DAC1=VRDC) are detected, the obtained power curve data (i.e., the detected DAC_Offset value and the laser power P1) is stored in a memory (a flash ROM or an EEPROM) of the optical disc device. When a laser power is to be set afterwards, a DAC input voltage corresponding to the laser power to be set can be detected using the stored power curve data.
For example, an input voltage (DAC1mW) for setting a playback laser power of 1 mW is detected using an equation“DAC1 mW=VRDC_Offset+(1 mW/P1)*(DAC1−VRDC_Offset)”.
The DAC_Offset value (i.e., the VRDC_Offset value) for setting the playback laser power is detected using the specific input voltage and the corresponding output laser power or the corresponding feedback voltage level as described above. However, a DAC_Offset value (i.e., VWDC_Offset) for setting a recording laser power must be additionally detected and stored when the optical disc device is an optical disc device for recording/playback. When a VWDC_Offset value has been detected and stored in the same method as the VRDC_Offset detection method and a laser power P1 actually output in response to a specific input voltage (DAC1=VWDC) higher than that of the VRDC value has been detected and stored in the laser power setting mode in the manufacturing process, a DAC input voltage corresponding to a recording laser power to be set afterwards can be detected using the stored values.
For example, an input voltage (DAC20mW) for setting a recording laser power of 20 mW is detected using an equation“DAC20 mW=VWDC_Offset+(20 mW/P1)*(DAC1−VWDC_Offset)”.
When power curve data has been detected and stored in the memory in such a manner in the manufacturing process of the optical disc device, the optical disc device can set a desired laser power level for recording or playback based on the stored power curve data afterwards and perform a desired recording or playback operation using the set laser power.
However, no power curve data may be present in a memory in an optical disc device (i.e., a power curve data storage area in the memory may be blank (0xffff)) when the optical disc device is shipped without laser power setting in the manufacturing process due to an operator's mistake, when the memory in which power curve data was stored has been reset or the data in the memory has been deleted, when an erasure or writing operation of the memory has failed, or when the optical disc device or a host connected to the optical disc device is powered off when data is being downloaded to the memory. If no power curve data is present in the memory, disc recognition is difficult and stable playback is also difficult due to inaccurate laser power setting. Recording on the disc readily fails during the recording. Even if recording on the disc is completed, high recording quality is not guaranteed.
Even when power curve data detected in the manufacturing process of the optical disc device is present in the memory, the power curve data may not be suitable due to changes in the characteristics of the optical disc device if much time has passed, thereby making it difficult to perform stable playback and recording operations.